Fix potential memory access violation in ecpg if filename of include file is

shorter than 2 characters.

Patch by: "Wu, Fei" <wufei.fnst@cn.fujitsu.com>

src/interfaces/ecpg/preproc/pgc.l

@@ -1538,7 +1538,7 @@ parse_include(void)
 		yyin = fopen(inc_file, "r");
 		if (!yyin)
 		{
-			if (strcmp(inc_file + strlen(inc_file) - 2, ".h") != 0)
+			if (strlen(inc_file) <= 2 || strcmp(inc_file + strlen(inc_file) - 2, ".h") != 0)
 			{
 				strcat(inc_file, ".h");
 				yyin = fopen(inc_file, "r");